This invention pertains to fuel cells containing electrolyte matrices and, in particular, to fuel cells containing such matrices and arranged in stack form.
In the design of fuel cells for use in a fuel cell stack, it is necessary to provide means to ensure that the matrix of each of the fuel cells receives an initial amount of electrolyte sufficient to provide electrochemical reaction. It is further necessary to provide means to ensure that the electrolyte lost during the operation of each cell is replenished. Failure to provide sufficient initial electrolyte and/or electrolyte replenishment reduces cell performance and can lead to cross over of reactant gases and attendant cell failure and, therefore, must be avoided.
Loss of electrolyte during fuel cell operation can occur in a number of ways. Thus, electrolyte is lost by being carried as a vapor from the cell by the reactant process gases. Also, the electrolyte volume is changed by changes in cell temperature and excess electrolyte at any given temperature is caused to leave the cell. This leaves insufficient electrolyte at later cell temperatures requiring increased electrolyte. Electrolyte loss also occurs due to other cell components which absorb electrolyte as they age.
Since, as above-noted, insufficient cell electrolyte reduces cell performance and can lead to cell failure, two basic approaches have been devised for ensuring proper filling and replenishing of electrolyte to the cell matrices. One approach looks to adding electrolyte to the matrices as wanted and another to storing all the needed electrolyte in the cell itself.
In one particular design embodying the second approach, an element of each cell (e.g., the anode electrode) is provided with a storage area for the electrolyte needed for replenishment. This typically requires that the cell component used for storage be thicker than would normally be the case. Since thicker cell components are undesirable, this design lends itself only to storage of a limited amount of electrolyte. Thus, replenishment can only be provided over a short term and not for the life of the cell.
Another design, this time embodying the first approach, makes use of a slot in the separator plate supporting the electrolyte matrix. This slot runs along an edge of the matrix and at opposite ends communicates with bores running through the plate. With the cells arranged in stack form the bores in each separator of each cell are placed in alignment. With this technique, however, it is possible for electrolyte to bypass a particular cell and, therefore, there is never assurance that electrolyte has been uniformly applied to each cell.
It is, therefore, an object of the present invention to provide a fuel cell assembly including electrolyte transport means adapted to ensure electrolyte communication with the cell matrix.
It is a further object of the present invention to provide a fuel cell assembly of the above-type which can be arranged in stack form with similarly adapted other fuel cells.